The present invention generally relates to microwave antennas and, more particularly, to a method for manufacturing a lens for use in a microwave antenna.
Various types of dielectric materials have been in use for a number of years. In one example, U.S. Pat. No. 2,716,190 to E. B. Baker discloses a xe2x80x9cdielectric material.xe2x80x9d This patent states that the invention disclosed therein relates to a dielectric material that consists essentially of small metal particles that are dispersed in a polymerized plastic matrix. The patent also states that the lens shown in FIGS. 1-2 of the patent has variations in dielectric constant that are achieved by compression molding the lens from a composite preform made from various samples of polystyrene containing differing proportions of aluminum or magnesium. The content of this patent is incorporated by reference into this application as if fully set forth herein.
In another example, U.S. Pat. No. 2,956,281 to E. B. McMillan et al. discloses xe2x80x9cdielectric walls for transmission of electromagnetic radiation.xe2x80x9d The patent states that one example of such a dielectric wall is a dielectric sheet wherein the dielectric constant increases from the faces to the interior. The content of this patent is incorporated by reference into this application as if fully set forth herein.
Dielectric materials have been utilized in a variety of different applications. One such example is U.S. Pat. No. 3,256,373 to R. L. Horst that discloses a xe2x80x9cmethod of forming a cylindrical dielectric lens.xe2x80x9d The patent states that the present invention disclosed therein contemplates the fabrication of a body of continuously varying dielectric constant material that is formed from, in one example, an artificial dielectric that consists of an array of randomly oriented metallic particles that are supported by a low density dielectric material. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 3,359,560 to R. L Horst discloses a xe2x80x9ccylindrical dielectric lensxe2x80x9d is yet another example of the use of dielectric material. This patent states that a microwave lens comprises a mass of dielectric beads supporting an array of randomly oriented insulated metallic slivers in the interstices between the beads. This patent also states that the concentration of slivers in the mass of beads is varied in certain desired directions to produce a smooth and continuous gradation in dielectric constant in these directions. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 3,866,234 to Gates, Jr. et al. discloses a xe2x80x9cshaped ceramic dielectric antenna lens.xe2x80x9d This patent states that one of the features of the invention disclosed in this patent is the provision of a rigidly-shaped lens body that is formed of a quantity of porous granules which are fused one to the other to provide the rigidity, each of the granules being essentially uniform in composition and size, and further having a pore size that is smaller than a minimum wavelength of the energy band to be transmitted. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 3,917,773 to Gates, Jr. et al. discloses a xe2x80x9cmethod for fabricating a shaped dielectric antenna lens.xe2x80x9d This patent states that a quantity of porous granules is formed from a particular ceramic composition which can be controlled to adjust the dielectric constant, the specific gravity, the hardness, and the temperature resistance of the lens formed by the granules. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 4,288,337 to Ota et al. discloses xe2x80x9clightweight materials having a high dielectric constant and their method of manufacture.xe2x80x9d This patent states that such materials are manufactured by mixing metal-coated expanded particles of plastic, glass or silica, thin-wall metal pipes or metal coated thin-wall plastic pipes and uncoated expanded particles of plastic, glass or silica, and then forming the resulting mixture into a desired shape by a thermal expansion process. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 4,482,513 to Auletti discloses a xe2x80x9cmethod of molding foam/aluminum flake microwave lenses.xe2x80x9d The patent states that such lenses are formed by preheating a mold that has a cavity of an appropriate configuration defined therein, filing the mold with a mixture of low density polyurethane foam components and fine aluminum flakes that are evenly distributed throughout the foam structure, and allowing the mixture to cool. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 5,096,551 to Schoen, Jr. et al. discloses a xe2x80x9cmetallized tubule-based artificial dielectric.xe2x80x9d This patent states that dielectric composites are formed by incorporating metallized particles having a high aspect ratio (such as metallized phospholipid tubules) in a polymeric and/or ceramic matrix, and then curing or sintering the resulting products in an electric or magnetic field to align the particles. The content of this patent is incorporated by reference into this application as if fully set forth herein.
U.S. Pat. No. 5,170,167 to Rix et al. discloses a xe2x80x9creflector for electromagnetic energy.xe2x80x9d The patent states that such reflectors include two lenses that are arranged such that electromagnetic energy from a source incident on the first lens is refracted onto the second lens and then is reflected from a reflective coating back towards the energy source. The patent states that the lenses are molded from silica flour in a polyester resin binder. The content of this patent is incorporated by reference into this application as if fully set forth herein.
Lens for use in microwave antennas typically are very hard to manufacture. One reason for this is that the typical aspect ratio and size of such a lens are very large. For example, a typical lens can be over twelve inches in diameter, three inches thick in the middle, and have sides that taper down to sharp edges. There is a continuing need for improved methods of manufacturing such lenses.
An exemplary microwave antenna lens is manufactured by providing a mold having a lens defining cavity formed therein, the shape of which is predetermined for a given application. The lens defining cavity is filled with a suitable filler material such as, for example, microspheres. A quantity of a resin is introduced into the lens defining cavity and fills the interstices between the individual pieces of filler material. Then, after the resin is cured, a microwave antenna is formed.
One aspect of the present invention is to provide certain protection for microwave lens that are manufactured. In one example, a thin film of a weatherable polymer is placed into the mold before the filler material and resin are introduced therein. A unitary mass is formed as the resin is cured.
In a further development of the invention, the polymer thin film is preformed to the proper shape that corresponds to the shape of the microwave lens to be formed, and is utilized in place of a separate mold. In this regard, the filler material and resin is introduced, in one exemplary application, directly into an interior space of the preformed thin film. One technique of forming the film is a thermoforming process. A further technique would be to precoat the surface of the mold with a resin that would harden to a film. This further technique can be performed, if desired, after a microwave lens is molded.
Certain features and advantages of the invention will become apparent from the description that follows.